Thermomechanical Fatigue Tests Research Articles

Cyclic deformation behaviors of Ti-46Al-2Cr-2Nb-0.15B alloy during thermo-mechanical fatigue tests

Thermo-mechanical fatigue tests were carried out on the gamma-TiAl alloy in the temperature range of 500-800 °C under mechanical strain control in order to evaluate its cyclic deformation behaviors at elevated temperature. Cyclic deformation curves, stress-strain hysteresis loops under different temperature-strain cycles were analyzed and dislocation configurations were also observed by TEM. The mechanisms of cyclic hardening or softening during thermo-mechanical fatigue (TMF) tests were also discussed. Results showed that thermo-mechanical fatigue lives largely depended on the applied mechanical strain amplitudes, applied types of strain and temperature. On the hysteresis loops appeared two apparent asymmetries: one was zero asymmetry and the other was tensile and compressive asymmetry. Dislocations configuration and slip behaviors were contributed to cyclic hardening or cyclic softening.

Experimental and Numerical Characterization of the Cyclic Thermomechanical Behavior of a High Temperature Forming Tool Alloy

This paper describes high temperature cyclic and creep relaxation testing and modeling of a high nickel-chromium material (XN40F) for application to the life prediction of superplastic forming (SPF) tools. An experimental test program to characterize the high temperature cyclic elastic-plastic-creep behavior of the material over a range of temperatures between 20°C and 900°C is described. The objective of the material testing is the development of a high temperature material model for cyclic analyses and life prediction of SPF dies for SPF of titanium aerospace components. A two-layer viscoplasticity model, which combines both creep and combined isotropic-kinematic plasticity, is chosen to represent the material behavior. The process of material constant identification for this model is presented, and the predicted results are compared with the rate-dependent (isothermal) experimental results. The temperature-dependent material model is furthermore applied to simulative thermomechanical fatigue tests, designed to represent the temperature and stress-strain cycling associated with the most damaging phase of the die cycle. The model is shown to give good correlation with the test data, thus vindicating future application of the material model in thermomechanical analyses of SPF dies for distortion and life prediction.

Thermomechanical fatigue of 1.4849 cast steel – experiments and life prediction using a fracture mechanics approach

AbstractIn this paper the thermomechanical fatigue properties of 1.4849 cast steel, which is used for exhaust manifolds and turbochargers, are investigated and a fracture mechanics based approach is used for fatigue life prediction. Isothermal low-cycle fatigue tests and thermomechanical fatigue tests are conducted in the temperature range from room temperature up to 1 000 °C. Fractographic investigations show that fracture occurs predominantly intergranularly at 600 °C, whereas mixed transgranular and intergranular crack growth is found otherwise. The methodology for fatigue life prediction is based on a time and temperature dependent cyclic plasticity model, which describes the transient stresses and strains, and on a law for time and temperature dependent microcrack growth. The crack growth law assumes that the increment in crack length in each cycle, da/dN, is correlated with the cyclic crack-tip opening displacement, δCTOD. An analytical fracture mechanics based estimate of δCTOD is used, which is derived for non-isothermal loadings. The fatigue lives of the low-cycle and the thermomechanical fatigue tests are predicted well with the model. Only predictions for the low-cycle fatigue tests at 600 °C, where integranular fracture is predominant, are non-conservative.

Thermo-mechanical fatigue behavior of the intermetallic gamma-TiAl alloy TNB-V5 with different microstructures

The cyclic deformation and fatigue behavior of the γ-TiAl alloy TNB-V5 is studied under thermo-mechanical load for the three technically important microstructures Fully-Lamellar (FL), Near-Gamma (NG) and Duplex (DP), respectively. Thus, thermo-mechanical fatigue (TMF) tests were carried out with different temperature-strain cycles, different temperature ranges from 400°C to 800°C and with two different strain ranges. Cyclic deformation curves, stress-strain hysteresis loops and fatigue lives are presented. The type of microstructure shows a surprisingly small influence on the cyclic deformation and fatigue behavior under TMF conditions. For a general life prediction the damage parameter of Smith, Watson and Topper PSWT is well suitable, if the testing and the application temperature ranges, respectively, include temperatures above the ductile-brittle transition temperature (approx. 750°C). If the maximum temperature is below that temperature, the brittle materials' behavior yields a high scatter of fatigue lives and a low slope of the fatigue life curve and therefore the damage parameter PSWT cannot be applied for the live prediction.

Temperature Calibration Techniques for TMF Testing

Abstract One of the methods to control the rapid temperature changes during a thermomechanical fatigue (TMF) test involves the use of an infrared pyrometer for temperature measurement. The infrared pyrometer relies on the emissivity of the test coupon. One way to determine this emissivity is to use a disappearing filament pyrometer. This paper presents two emissivity calibration techniques: Strain measurement and application of non-permanent thermocouples. Both techniques were applied for TMF testing, and the advantages and disadvantages of these techniques are described. The results show that the temperature indicated by these methods can significantly differ when compared to the actual temperature of the test specimen measured by thermocouples. However, these variances can be mitigated by calibration.

Cyclic thermo-mechanical material modelling and testing of 316 stainless steel

A programme of cyclic mechanical testing of a 316 stainless steel, at temperatures of up to 600 °C under isothermal conditions, for the identification of material constitutive constants, has been carried out using a thermo-mechanical fatigue test machine (with induction coil heating). The constitutive model adopted is a modified Chaboche unified viscoplasticity model, which can deal with both cyclic effects, such as combined isotropic and kinematic hardening, and rate-dependent effects, associated with viscoplasticity. The characterisation of 316 stainless steel is presented and compared with results from tests consisting of cyclic isothermal, as well as in-phase and out-of-phase thermo-mechanical fatigue conditions, using interpolation between the isothermal material constants to predict the material behaviour under anisothermal conditions.

Mechanism-based thermomechanical fatigue life prediction of cast iron. Part II: Comparison of model predictions with experiments

In the present paper, predictions of mechanism-based models for cast iron are compared to experimental results obtained for the nodular cast iron EN-GJS-700, the vermicular cast iron EN-GJV-450 and the lamellar cast iron EN-GJL-250. A strategy is proposed to efficiently identify the model parameters based on isothermal experiments. In particular, complex low cycle fatigue (LCF) tests, tension tests and compression tests are used to adjust the time and temperature dependent cyclic plasticity model. The time and temperature dependent fatigue life prediction model is adjusted to LCF tests. For all investigated cast iron materials, good predictions of thermomechanical fatigue (TMF) tests are possible with the models. Additionally, the location of failure and fatigue life of a thermomechanically loaded double-sided notched specimen are predicted with high accuracy.

Thermomechanical Fatigue Behavior of the Intermetallic γ-TiAl Alloy TNB-V5 with Different Microstructures

The cyclic deformation and fatigue behavior of the γ-TiAl alloy TNB-V5 is evaluated under thermomechanical load for three different microstructures. For this purpose, strain-controlled thermomechanical fatigue (TMF) tests were carried out with different temperature-strain cycles, different temperature ranges from 400 °C to 800 °C (673 K to 1073 K), and with two different strain ranges to set a fatigue-life relation. Cyclic deformation curves, stress-strain hysteresis loops, and fatigue lives of the tests are presented. The microstructures near-gamma (NG) and duplex (DP) show comparable fatigue lives under all test parameters. The microstructure fully-lamellar (FL) offers longer fatigue lives at the same loading conditions. For a general life prediction, the damage parameter of Smith, Watson, and Topper, P SWT vs fatigue life, is well suitable, if the testing and the application temperature ranges, respectively, include temperatures above the ductile-brittle transition (approximately 750 °C). In the completely brittle material behavior regime the quality of the lifetime prediction is unacceptable. The damage parameter P HL by Haibach and Lehrke shows a comparable correlation to the fatigue life as P SWT. The results are discussed with microstructural investigations.

Effect of NiCoCrAlY+Re coatings on TMF behaviour of first and second generation single crystal Ni based superalloys

<title/>Thermomechanical fatigue (TMF) tests were carried out on first and second generation single crystal Ni based superalloys both uncoated and with NiCoCrAlY+Re thermal spray coatings. Microstructural evaluations were performed to elucidate the damage evolution mechanisms and the influence of alloy chemistry and coating presence on TMF life. In uncoated and coated materials, bands of localised strain and consequent twinning appear to be the main deformation mechanism. The first and second generation superalloys show similar behaviour, although damage evolution has a different kinetic rate. Coating appears to be beneficial to TMF life, probably due to a more homogeneous distribution of damage along the gauge length.

Advanced thermomechanical fatigue crack growth testing for component life validation

Abstract The increasing performance requirements of gas turbines are driving higher operating temperatures in critical components, leading to greater creep and fatigue interactions. There is thus a requirement for thermomechanical fatigue (TMF) test data, including TMF crack growth rates. The test equipment required to meet this challenge is briefly discussed, along with the development of the test methodology. Thus, the accurate measurement and maintenance of thermal performance during TMF are considered. The determination of fatigue crack growth rates by conventional electrical potential difference measurements has been employed, utilising convenient dwells within the TMF cycles, where both load and temperature are held constant for a brief period. These experimental methods have been demonstrated with trials on the advanced nickel base superalloy RR1000 used for turbine discs. This work has also highlighted significant microstructural effects on the crack growth rates, with the coarser grain siz...

Innovative testing concept of cylinder heads

The increasing demands for improving the specific power output of modern power-trains and for reducing the component weight via lightweight design, require detailed expertise about the damage mechanisms occurring under real service loading conditions. Taking into account requirements for accelerated, cost-effective component testing and damage analysis, IABG developed a new test stand for thermo mechanical fatigue testing of cylinder heads. Thereby, both the test and development process of cylinder heads may be accelerated significantly. The implementation of an in-situ crack detection system enables the investigation of crack initiation and propagation as well as a 24 / 7 service of the test stand.

Novel induction heating system for service cycle thermo-mechanical fatigue testing

The concept of an active/passive coil arrangement has been devised as part of the development of a flexible induction heating system to provide well controlled temperature distributions during complex service cycle thermo-mechanical fatigue tests involving low alloy bainitic and martensitic steels. Introducing a passive coil at the mid-specimen gauge length position is responsible for a significant reduction in axial temperature gradient during thermal transients. The effectiveness of this novel new arrangement is demonstrated and the possibilities for further enhancement are explored.

A new low cycle fatigue criterion for isothermal and out-of-phase thermomechanical loading

A new multiaxial low cycle fatigue criterion based on a damage parameter is presented as an attempt to condition energy based approaches for the general common use in isothermal and thermomechanical out-of-phase loading. The damage parameter is based on the dissipated plastic strain energy per cycle, with a stress correction factor to account for mean and maximum stress influences, and a thermal term to account for elevated temperature damages. With such a formulation, the low temperature damaging regime (dislocations glide) can be separated from the high temperature one (diffusion processes). Oxidation and creep damages are accounted for in an implicit manner. The prediction capability of the present criterion is compared with that of other classical lifetime criteria using data from uniaxial isothermal and out-of-phase thermomechanical fatigue (TMF) tests performed on three cast iron families which are relevant for different internal combustion engine components. The result is higher prediction accuracy and a capability to estimate TMF lifetime by calibrating on isothermal fatigue tests only, leading to a great potential cost saving for future test programs given similar materials and loading conditions.

Determination of Material Parameters in the Chaboche Unified Viscoplasticty Model

An experimental programme of cyclic mechanical testing of a 316 stainless steel, at temperatures up to 600°C, under isothermal conditions, for the identification of material constitutive constants, has been carried out using a thermo-mechanical fatigue (TMF) test machine with induction coil heating. The constitutive model adopted is a modified Chaboche unified viscoplasticity model, which can deal with both cyclic effects, such as combined isotropic and kinematic hardening, and rate-dependent effects, associated with viscoplasticity. The characterisation of 316 stainless steel is presented and compared to results from cyclic isothermal tests. A least squares optimisation algorithm has been developed and implemented for determining the material constants in order to further improve the general fit of the model to experimental data, using the initially obtained material constants as the starting point in this optimisation process. The model predictions using both the initial and optimised material constants are compared to experimental data.

Thermomechanical Fatigue Behavior of Bare and Coated CMSX-4

Highly cooled turbine blades undergo very high thermal gradients during rapid engine idle-max-idle cycling. Traditional isothermal fatigue data are often insufficient for predicting service lives. A complete set of high temperature tests, in the range of 750–1050°C, was performed on single crystal alloy CMSX-4. The test program comprised tensile, creep, low cycle fatigue, and thermomechanical fatigue (TMF) tests. In particular the cycle time for TMF was 3 min, aiming to simulate the real high-power transient conditions in aircraft engines. Clockwise and counterclockwise diamond cycle types were applied on bare and coated specimens to investigate their influence on the fatigue limit. The comparison of the results obtained with the available ones from open literature is discussed.

Determination of material properties in the Chaboche unified viscoplasticity model

An experimental programme of cyclic mechanical testing of a 316 stainless steel, at temperatures up to 600°C, under isothermal conditions, for the identification of material constitutive constants, has been carried out using a thermo-mechanical fatigue (TMF) test machine with induction coil heating. The constitutive model adopted is a modified Chaboche unified viscoplasticity model, which can deal with both cyclic effects, such as combined isotropic and kinematic hardening, and rate-dependent effects, associated with viscoplasticity. The characterization of 316 stainless steel is presented and compared with results from cyclic isothermal tests. A least-squares optimization algorithm has been developed and implemented for determining the material constants in order to further improve the general fit of the model to experimental data, using the initially obtained material constants as the starting point in this optimization process. The model predictions using both the initial and optimized material constants are compared to experimental data.

Crack appearance of single-crystal nickel-base superalloys after thermomechanical fatigue failure

Thermomechanical fatigue (TMF) testing was conducted on single-crystal nickel-base superalloys. Distinct cracking behaviors were found to occur under different cycling conditions. A crack generally initiates from the specimen surface. For the TMF cycling without a compressive hold time, the crack initially grows perpendicular to the stress axis and then propagates along a twin plate. For the TMF cycling with a compressive hold time, the main crack propagates directly along a twin plate until final failure.

Effects of Underfill Materials and Thermal Cycling on Mechanical Reliability of Chip Scale Package

The thermomechanical reliability of chip-scale packages (CSPs) with various underfills was evaluated by measure the electrical resistance under thermal shock and four-point bending fatigue tests. The underfill containing cycloaliphatic-type epoxy resin had lower resistance than without cycloaliphatic-type epoxy resin under thermomechanical fatigue test because the cycloaliphatic-type epoxy resin was able to mechanically relax more than the other types. The lifetimes of the CSPs under thermomechanical fatigues were strongly dependent on the properties of the underfill.

Fatigue of the Near-Alpha Ti-Alloy Ti6242

Ti6242 is the workhorse of high-temperature Ti-alloys in the high pressure compressor of aero engines. In this study the influence on isothermal fatigue of different load controls, i.e. stress, total strain and plastic strain control at different temperatures and environments was investigated. The alloy had a bi-modal microstructure (some 30 vol.% primary alpha), which yields a good balance between fatigue and creep properties. In addition thermomechanical fatigue (TMF) tests were also performed. Modelling lifetime on the basis of a Basquin–Coffin–Manson relationship revealed only marginal scattering in the temperature range between 350°C and 650°C. Increasing the temperature led to a decrease in lifetime. This can be attributed to increased oxidation and creep. The latter one is clearly seen in isothermal tests under stress control. Tests in vacuum resulted in longer lifetimes. In-phase TMF tests exhibited a longer lifetime than out-of-phase tests, with a factor of about 4. Lifetime and stress response of in-phase tests are similar to the corresponding lifetime of an isothermal test at the maximum temperature. This similarity can be considered as a starting point for modelling TMF behaviour on the basis of isothermal fatigue.

OS0713 コールドスプレーにより作製した準結晶粒子分散アルミ合金コーティング材の熱疲労挙動(構造用材料の疲労挙動と寿命評価,オーガナイズドセッション)

For the purpose of the partial strengthening of the substrate, the aluminum alloy coating with dispersed nanoscale quasicrystalline particles produced by cold spray was developed. In this research, the thermo-mechanical fatigue behavior of the coating was evaluated. The cold spray was carried out on condition of the gas temperature 673K and gas pressure 3MPa. Out-of-phase type thermo-mechanical fatigue (TMF) tests were performed for the AC2B-T6 substrate samples and the coating samples with the temperature range of 323-523K. According to evaluation of the coating, there is no void at internal coating and the interface between coating and substrate. It was clear that there is the tendency of improvement of the thermo-mechanical fatigue lives by the cold spray coating compared with the substrate samples. It was suggested that the improvement of the TMF lives was due to the suppression of the initiation or the propagation of the surface cracks of the substrate by the coating.